PORT Adelaide's dual All Australian midfielder Robbie Gray could miss the next three weeks with a hamstring injury.

Gray was one of five changes to the Power's side for Saturday night's crucial clash with fellow strugglers Richmond at the MCG.

Port midfield manager Michael Voss told 5AA that the speedy midfielder injured his hamstring during a training session on Wednesday night.

''We think it might be between two to three weeks,'' Voss said.

"It's never great when it's midweek.

"That's still to be assessed, so I'm sure they'll do that over the next 24 hours and be a bit clearer.''

The two-time reigning club best and fairest is averaging 25.6 disposals per game to go with seven goals for the season.

Forward Chad Wingard is also out with concussion and Karl Amon has been dropped, but the biggest surprise is the axing of ruckman Matthew Lobbe.

Lobbe has been sent back to the SANFL to get more involved in general play.

That leaves the ruck duties on the shoulders of second-gamer Dougal Howard, while key forward Charlie Dixon will also pinch-hit in the middle of the ground.

Voss said Port wanted to see Lobbe regain his confidence with a stint with the Magpies.

"Sometimes you need a bit of time to go back and re-gather some of that form,'' Voss said.

"We feel like his ruck work has been competitive and there's some other things in his game that he needs to work on.

"Being able to go back to the SANFL and work on a few things without having the high pressure of AFL football (will be beneficial).

''We've got a few others around him who aren't in great form.

''We'd like a greater involvement (around the ground) from him and we feel Dougal Howard's been doing a really strong job.'

While Lobbe is contributing 31.4 hit-outs per game, he has averaged just eight disposals and 1.6 marks through the opening five rounds.

Along with Howard, Jared Polec, Brendon Ah Chee, Jarman Impey and Nathan Krakouer have been recalled to the senior side.

Krakouer returns without playing any footy in the SANFL after a club-imposed five-week suspension for an off-field incident in Perth.

Wingard finished last weekend's loss to Geelong, but showed symptoms of a concussion after the game.

Port's head of high performance Darren Burgess told the club's website: “We take concussion seriously, and we’ll need to have Chad reviewed again next week, which is a standard procedure when we can’t clear him to play this weekend.

“We’re hopefully he’ll get the tick and be cleared to play against Brisbane.”

The Power have come under intense scrutiny after consecutive heavy defeats to GWS and Geelong.